Arc furnace crucible

ABSTRACT

AN ARC FURNACE CRUCIBLE HAVING A CENTRAL RECESS. A PREFORMED, CONICALLY-TAPERED PLUG OF THE MATERIAL TO BE MELTED IS SECURED WITHIN THE RECESS IN GOOD ELECTRICAL CONNECTION WTH THE INNER WALL OF THE CRUCIBLE. THE PLUG OF MATERIAL TO BE MELTED MAY BE EMPLOYED AS THE STARTING MATERIAL FOR THE ARC FURNACE AND WILL THEREAFTER INSURE GOOD ELECTRICAL CONDUCTIVITY BETWEEN HE CRUCIBLE AND THE MELT. ACCORDING TO A SECOND EMBODIMENT OF THE PRESENT INVENNTION, AN ARC FURNACE CRUCIBLE IS PPROVIDED WITH A LINER OF REFRACTORY MATERIAL COVERING THE SIDEWALLS OF THE CRUCIBLE. THE REFRACTORY LINER FUNCTIONSTO MINIMIZE HEAT CONDUCTION FROM THE MELT TO THE CRUCIBLE, THUS IMPROVING THE THERMAL EFFICIENCY OF THE ARC FURNACE. A LAYER OF HEAT INSULATING MATERIAL MAY BE DISPOSED BETWEEN THE REFRACTORY LINER AND THE CRUCIBLE TO FURTHER MINIMIZE HEAT LOSS.

Feb. 20, 1973 P. SCHLIENGER I 3,717,713

ARC FURNACE CRUCIBLE Filed F eb. 18., 1971 2 Sheds-Sheet 1 INVENTOR. MAXF? SCHLIENGER 7 ATTORNEYS .FeB..20, 1973 v M. P. SCHLIENGER 3,717,7l3

ARC FURNACE CRUCIBLE Filed Feb. 18, 1971 2 Sheets-Sheet 2 FIG 2INVENTOR. MAX P SQHLIENGER v Ml ATTHDMCVQ United States Patent OficeABSTRACT OF THE DISCLOSURE An arc furnace crucible having a centralrecess. A preformed, comically-tapered plug of the material to be.

melted is secured Within the recess in good electrical connection withthe inner wall of the crucible. The plug of material to be melted may beemployed as the starting material for the arc furnace and willthereafter insure good electrical conductivity between the crucible andthe melt. According to a second embodiment of the present invention, anarc furnace crucible is provided with a liner of refractory materialcovering the sidewalls of the crucible. The refractory liner functionsto minimize heat conduction from the melt to the crucible, thusimproving the thermal efficiency of the arc furnace. A layer of heatinsulating material may be disposed between the refractory liner and thecrucible to further minimize heat loss.

This invention relates to are furnace crucibles.

Arc furnaces generally incorporate a melt contained within a crucibleand an electrode which is arranged to establish an arc to the melt inorder to create a sufficient temperature gradient to melt materials. Onecommonly employed technique utilizes a previously molded, consumableelectrode, in which the electrode itself constitutes the material whichis to be melted. In other applications where powder or sponge materialis to be melted, a nonconsumable electrode is employed to create therequisite arcs. In all of such are furnaces, the arcs result from theapplication of a high electrical potential difference between theelectrode and the melt. Generally, a conductive crucible is employed,electrical connection to the melt being achieved by connecting onepolarity of an electrical source to the crucible.

In such arc furnaces it is important to establish good electricalconductivity between the crucible and material contained therein.Specifically, poor electrical connection between the melt and thecrucible will result in the formation of one or more secondary arcsbetween the melt and the crucible, which arcs will cause the erosion anddeterioration of the crucible. Typically such poor electrical connectionbetween the crucible and the melt occurs when the skull, or remnant ofthe previous melt which lines the inside of the crucible, becomesoxidized due to the presence of air in the furnace, which oxidepossesses a high electrical resistance. Alternatively, poor electricalconnection between the melt and the crucible may result from shrinkageof the skull due to the cooling thereof, thus resulting in a physicalseparation between the skull and crucible.

In addition, conventional metallic arc furnace crucibles suffer fromconsiderable heat losses through conduction of melt heat to thecrucible. This unduly burdens the crucible cooling system and results inlow thermal efficiency, and thus inetficient arc melting.

These drawbacks are overcome in accordance with the present invention byproviding an arc furnace crucible having a central recessed cavity. Apre-forrned conically tapered plug of the material to be melted issecured within this cavity in good electrical connection with the innerwall of the crucible. The plug of material to be melted is 3,717,713Patented Feb. 20, 1973 employed as the starting material for the arcfurnace. In this manner, the plug will melt and become an integral partof the crucible skull. Thereafter, good electrical contact between theskull and the crucible is assured by the attachment of the plug withinthe cavity in the crucible.

In accordance with another embodiment of the present invention, there isprovided an arc furnace crucible having a liner of refractory materialcovering the side walls of the crucible. Such a refractory liner willfunction to minimize heat loss through the side walls of the crucible,thus increasing the efiiciency of the arc furnace. The refractory linermay be extended to cover a portion of the bottom of the crucible, andmay be employed with a crucible incorporating the starting plug ofmaterial to be melted referred to hereinbefore. In addition, a layer ofheat insulating material may be disposed between the re- 1fractory linerand the crucible to further minimize heat oss.

It is thus an object of the present invention to provide an arc furnacecrucible particularly adapted to establish good electrical conductivitybetween the crucible and the material to be melted.

Another object of the present invention is to provide an arc furnacecrucible having a central recessed cavity and a preformed plug of thematerial to be melted secured within the cavity, the plug of material tobe melted being employed as the starting material of the arc furnace.

Yet another object of the present invention is to provide an arc furnacecrucible that is particularly adapted to minimize heat losses and thusimprove the efiiciency of the arc furnace.

Still another object of the present invention is to provide an arcfurnace crucible having a liner of refractory material covering the sidewalls of the crucible.

These and other objects, features and advantages of the presentinvention will be more readily apparent from the following detaileddescription with reference to the accompanying drawings, wherein:

FIG. 1 is a side cross-sectional view of an arc furnace crucibleaccording to a preferred embodiment of the present invention; and

FIG. 2 is a side cross-sectional view, similar to FIG. 1, of anotherembodiment of the present invention.

Referring initially to FIG. 1, there is provided an arc furnace crucible15 having an outer housing 16 and an inner metallic crucible shell 17.The peripheries of housing 16 and crucible shell 17 are engaged,crucible shell 17 being disposed within housing 16, and an O-ring orother suitable seal 18 is disposed therebetween to insure fluid tightmating thereof. The central portion of crucible shell 17 comprises adownwardly extending tubular flange por tion 17a which is engaged with acentral aperture in housing 16. A plurality of O-rings or seals 19 aredisposed between the flange portion 17a of crucible shell 17 and thecentral aperture of housing 16, insuring fluid-tight engagement thereof.Thus, crucible shell 17 and housing 16 are centrally and peripherallyengaged to define a hollow crucible interior.

Access to an exit from the hollow interior thus defined between crucibleshell 17 and housing 16 is respectively provided by an intake port oraperture 20 and an exhaust port or aperture 21 in housing 16. Disposedwithin the hollow interior defined by crucible shell 17 and housing 16is a bafile 22. Baffle 22 includes a plurality of ducts or passages 22a.A diagonally-oriented angular ring 23 is disposed between baffle 22 andhousing 16, bafile 22 and ring 23 cooperating to define a coolant fluidpath as indicated by the arrows on FIG. 1. Thus, coolant fluid may beintroduced into intake port 20 and exited from exhaust port 21, so tocool crucible shell 17. The foregoing crucible cooling system is old inthe art, and is described herein for illustrative purposes only, itbeing understood that the arc furnace crucible according to the presentinvention may be employed with alternative conventional cooling systems.

The interior of the downwardly extending tubular flange portion 17acomprises a stepped cylindrical aperture defining two bore portions 25and 26, the upper bore portion 25 being of somewhat greater diameterthan the lower bore portion 26. Disposed within the upper bore 25 is anannular ring 27 of wedge-shaped cross-section. A conically tapered plug28 of the material to be melted is disposed within annular ring 27. Inparticular, plug 28 is threadibly attached to a shaft 29. A nut 30 atthe other end of shaft 29 bears against a disc or bottom plate 31 tourge plug 28 downwardly into ring 27. Preferably, but not necessarily,ring 27 may comprise a segmented copper ring, so that as plug 28 isurged downwardly, ring 27 will expand somewhat to provide tightmechanical fit between plug 28, ring 27 and bore 25. In this manner, oodelectrical conductivity between crucible shell 17 and plug 28 isassured. Furthermore, provision of a segmented annular ring 27 assistsin the removal of plug 28, should this be desired. Typically, removal ofplug 28 would be necessary if the material to be melted is to bechanged. In order to accomplish such removal, nut 30 may be removedallowing ring 27 to contract, and thus permitting plug 28 and ring 27 tobe vertically withdrawn from bore 25.

Preferably, but not necessarily, plug 28 is of sufiicient length tovertically project above the bottom of crucible shell 17, so that if anelectrode is disposed in proximity to the bottom of crucible shell 17, apreferred path of arcing will exist between the electrode and plug 28.As will be described in greater details hereinafter, plug 28 may thus beadvantageously employed as the starting point or starting material ofthe arc furnace.

A disc 32 is mounted within bore 26 by a retaining ring 33. Disc 32 isthus disposed beneath plug 28 and functions as a chill plate forsolidifying melt material impingent thereon, should plug 28 melt.Accordingly, the leakage of melt material will be substantiallyprevented.

In operation, an electrode (not shown in FIG. 1) of either theconsumable or nonconsumable types is initially disposed adjacent plug28. A source of high energy electrical power is provided, the respectivepolarities of which are connected to the electrode and crucible 15. Thisobviously establishes a high energy potential difference between theelectrode and crucible 15, causing one or more arcs to be developed fromthe electrode to plug 28. The arcs, of course, create a sufiicienttemperature to cause the desired melting action. Simultaneously with theforegoing melting action, coolant fluid may be introduced into intakeport 20 and exited from exhaust port 21 to accomplish cooling ofcrucible shell 17.

As the arc meting progresses, the arc furnace crucible 15 may thereafterbe employed in a conventional manner. However, by providing a plug 28 ofmelt material, and starting the arc thereon, damage to the crucible dueto secondary arcing is substantially eliminated. Furthermore, plug 28will thereafter form an integral part of the skull or remnant of meltmaterial left within crucible shell 17, so that good electricalconductivity between the skull and the crucible will be assured.

Referring now to FIG. 2, there is provided an arc furnace crucible 40according to another embodiment of the present invention. Specifically,there is provided an outer housing 41 and an inner metallic crucibleshell 42, housing 41 and crucible shell 42 being engaged in the samemanner described with respect with the embodiment depicted in FIG. 1.Thus, crucible shell 42 and housing 41 are centrally and peripherallyengaged to define a hollow crucible interior.

Access to an exit from the hollow interior thus defined is respectivelyprovided by an intake port or aperture 43 and an exhaust port oraperture 44 in housing 41. Disposed within the hollow interior is abaffle 45 and a diagonally-oriented annular ring 46, which function todefine a path of coolant flow indicated by the arrows in FIG. 2,substantially identical to that described with respect to the embodimentdepicted in FIG. 1.

A conically tapered plug 47 of the material to be melted may be mountedin the bottom of crucible shell 42, substantially as described withrespect to the embodiment of the present invention depicted in FIG. 1.Alternatively, plug 47 may be omitted and a conventional flat metalliccrucible bottom provided.

According to this embodiment of the present invention, a crucible liner48 of refractory material may be provided within crucible shell 42.Refractory liner 48 may be retained in crucible shell 42 by a pluralityof retaining brackets 50. As depicted in FIG. 2, refractory liner 48 maycompletely cover the side walls of crucible shell 42, and may extendhorizontally to cover a portion of the bottom thereof. Refractory liner48 functions to reduce the conduction of heat from the melt to thecrucible, thus improving the thermal efliciency of the arc furnace.Additionally, an insulating layer 49 may be disposed between refractoryliner 48 and crucible shell 42 to further minimize such heat losses.Preferably, but not necessarily, the bottom surface of crucible shell 42includes a suitable recess for the periphery of refractory liner 48 andinsulating layer 49, so as to form a smooth crucible bottom.

In operation, crucible 40 may be employed in substantially the samemanner described with respect to the embodiment of the present inventiondepicted in FIG. 1. However, the conduction of heat from the melt to thecrucible will be minimized by refractory liner 48 and insulating layer49, thus improving the thermal efficiency of crucible 40 by minimizingsuch heat losses.

While particular embodiments of the present invention have been shownand described, it is apparent that adaptations and modifications may bemade without departing from the true spirit and scope of the presentinvention, as set forth in the claims.

What is claimed is:

1. An arc furnace crucible comprising a crucible shell having a taperedrecess in the bottom thereof, a downwardly tapering frusto-conical plugof the material to be melted, a shaft secured to the bottom of saidplug, and means drawing said shaft downwardly within said recess forreleasably engaging said plug in said recess.

2. Apparatus according to claim 1 comprising a metallic annular ring ofwedge-shaped cross section complementary to the taper of said plugdisposed within and defining said recess, said plug being engaged withinsaid annular ring.

3. Apparatus according to claim 2 wherein said annular ring issegmented.

4. Apparatus according to claim 1 wherein said plug extends upwardlyabove the bottom surface of said crucible shell.

5. Apparatus according to claim 1 wherein the lower end of said shaft isthreaded and said means urging said shaft downwardly comprises a nutthreadably engaging the lower end of said shaft.

6. Apparatus according to claim 1 wherein said crucible shell ismetallic and further comprising a liner of refractory material disposedwithin said crucible shell, said liner substantially covering at leastthe sidewalls of said crucible shell.

7. Apparatus according to claim 6 comprising a layer of heat-insulatingmaterial disposed between said liner and said crucible shell.

8. In a melting and casting arc furnace of the type having an enclosedhousing forming a controlled ambient atmosphere, a crucible mounted insaid housing for containing a melt and an electrode adapted to producean arc to the melt, the improvement comprising: a downwardly taperingfrusto-conical plug of the material to be melted disposed in a taperedrecess in the bottom of said crucible, a shaft secured to the bottom ofsaid plug and means drawing said shaft downwardly within said recess forreleasably engaging said plug in said recess.

9. Apparatus according to claim 8 comprising a metallic annular ring ofwedge-shaped cross section complementary to the taper of said plugdisposed within and defining said recess, said plug being engaged withinsaid annular ring.

10. Apparatus according to claim 9 wherein said annular ring issegmented.

11. Apparatus according to claim 8 wherein said plug extends upwardlyabove the bottom surface of said crucible shell.

12. Apparatus according to claim 8 wherein the lower end of said shaftis threaded and said means urging said shaft downwardly comprises a nutthreadably engaging the lower end of said shaft.

13. Apparatus according to claim 8 wherein said crucible shell ismetallic and further comprising a liner of refractory material disposedwithin said crucible shell, said liner substantially covering at leastthe sidewalls of said crucible shell.

14. Apparatus according to claim 13 comprising a layer 6 ofheat-insulating material disposed between said liner and said crucibleshell.

15. An arc furnace crucible comprising a crucible shell having a recessin the bottom thereof, a plug of the material to be melted complementaryto said recess, a shaft secured to the bottom of said plug, extendingdownwardly through an aperture in said crucible and drawing means onsaid shaft below said crucible drawing said shaft downwardly Within saidrecess for releasably engaging said plug in said recess.

References Cited UNITED STATES PATENTS 2,297,560 9/ 19 421 Hopkins13----'32 X 1,778,578 10/1930 Baily 13-9 ES 1,310,341 7/1919 Hutchins13-32 X 2,761,002 8/1956 Laird et a1 13-9 2,899,667 8/1959Bredtschneider et al. 13-9 X 3,129,473 4/1964 Veil, Jr 13-9 X ROY N.ENVALL, JR., Primary Examiner US. Cl. X.R.

